Many modern e-mail clients provide a local cache for fast and offline access to e-mail messages and other data. Such local cache may include a complete copy of a user's mailbox that is also stored on an e-mail server. Over the last decade, mailbox storage quotas have grown exponentially, and are now many gigabytes in size. For the majority of users, there is little or no utility in providing offline access to extremely old data. Moreover, because mailboxes have become so large, it has become increasingly unwieldy to download mailbox data from an e-mail server as well as increasingly difficult to operate on such data locally without significantly impacting performance. Also, if the device upon which the e-mail client is installed has a limited storage footprint (as is the case with many modern mobile devices), then the local cache may consume an unacceptable amount of the available storage space.
Some mobile e-mail clients attempt to address the foregoing issues by downloading and locally storing only a subset of a user's e-mails that are available on an e-mail server. Such subset may be defined in terms of a rolling time window. For example, only e-mails received over the past seven days may be maintained in a local cache at any given time. In certain implementations, the size of the time window may be fixed, while in other implementations, the size of the time window may be configurable by a user.
Although such mobile e-mail clients are able to limit the storage requirements of the local cache by downloading only the most recently-received e-mails, these e-mail clients do not provide a user with affordances or any information about the state of older e-mail messages that reside only on the e-mail server. Typically, such older e-mail messages can only be accessed by widening the time window (in those implementations that support a configurable time window), by running a search against such older e-mails, or by incrementally downloading more items. In each case, copies of the older e-mails must be stored in the local cache, thereby consuming additional storage space on the user's mobile device.
The features and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the corresponding reference number.